1. Field of the Invention
This invention relates to Vitamin D.sub.3 derivatives of the following formula (I) ##STR2## wherein R represents a hydrogen atom or a lower alkyl group.
2. Prior Art
It has been known that 1.alpha.25-dihydroxy-vitamin D.sub.3, which is a hormonal metabolite, is the biological active form of vitamin D.sub.3 in intestinal calcium transport and bone calcium resorption (cf. Merck Index, 1612:-Calcitriol) and, it has recently found that 1.alpha.25-dihydroxyvitamin D.sub.3 has an anti-tumor effect against human leukemia-derived cells, etc. (cf. unexamined Japanese patent publication laid-open under the laying-open No. Sho.57-149224 or 58-206525).
22,25-dihydroxyvitamin D.sub.3 is also a known compound, but this compound has been known to possess neither vitamin D activity nor antivitamin D activity, and it is not known whether this compound have an anti-tumor activity.